The present invention relates to circulators and isolators.
Ferrite circulators are for instance used in microwave applications in order to separate incoming and outgoing signals. They are also used as isolators, switches and phase shifters. The functionality of the circulator has been described for instance in the following articles: xe2x80x9cOn the principle of stripline circulationxe2x80x9d, by H. Bosma, The Institution of Electrical Engineers, No. 3689, Jan 1962; xe2x80x9cOperation of the Ferrite junction Circulatorxe2x80x9d by C. E. Fay and R. L. Comstock, IEEE transactions on microwave theory and techniques, Jan. 1965; and xe2x80x9cWide Band Operation of Microstrip Circulatorsxe2x80x9d, Y. S. Wu and F. Rosenbaum, IEEE transactions on microwave theory and techniques, Vol. MTT-22, No. 10, Oct. 1974.
Circulators having three ports disposed with 120xc2x0 between them show particular beneficial properties. Therefore, if a higher number of ports than three is needed, a plurality of such three-port circulators are typically interconnected.
Prior art document U.S. Pat. No. 5,347,241 discloses a four port circulator comprising two coaxially arranged three port circulators. The three port circulators are formed on a combination of ferrite and ceramic substrates having a conductive strip layer printed thereon. One embodiment includes a common magnet providing magnetic field through the circulators. Another embodiment comprises two magnets arranged on each side of a magnetic shielded carrier providing magnetic fields through the circulators. The above circulator is useful for wide-band active array antennas.
FIG. 6 of the present application is a representation of U.S. Pat. No. 5,347,241 in which a four port circulator is used as a protection device for a transmit and receive module (TRM) for a radar system.
Prior art document JP-A-09289403 shows a microwave circulator formed by a ferrite substrate and by two magnets being arranged on opposite sides of the substrate.
Prior art document WO-0 079 845 shows a multi-layer circuit board that is arranged as a dual symmetrical strip line configuration whereby top and bottom ground planes enclose the substrate layers as well as a centre ground plane. Among the three ground planes, two signal strip layers are provided. Thereby, microwave emissions can be kept at a minimum. The substrate layers are provided with apertures with an increasing diameter from bottom to top for accommodating the insertion of components in the substrate within the shielded area, whereby two components can be inserted above one another. One component is arranged on the shoulders that are formed by the differently sized apertures. The components are electrically connected to micro strips on the circuit layers by wire bonding.
Prior art document EP-0 996 188 shows a transmit circuit, a receive circuit and a circulator being formed on a Monolithic Microwave Integrated Circuit (MMIC) substrate in strip line configuration, whereby the circulator comprises a ferrite element being embedded or mounted on the MMIC substrate. As ferrite element, Sr/Br magnetoplumbite hard ferrite is proposed, whereby an external magnet is not needed due to the self-coercive force of this material. The size of the apparatus is thereby reduced. However, the above self-coercive materials are not adapted for high power applications.
Prior art document U.S. Pat. No. 4,058,780 shows a four port circulator being formed by two interconnected rectangular port hollow tube circulators being arranged adjacent to one another in the same plane and being interconnected by a common port. Each circulator is provided with a gyro-magnetic cylindrical element providing for the non-reciprocal circulation.
It is a primary object of the present invention to provide a circulator unit which is compact and shielded and which can be integrated in or easily coupled to circuits comprising monolithic microwave integrated circuit (MMIC) devices which are produced with usual microwave circuit production means.
This object has been accomplished by the subject matter defined by claim 1.
It is a further object to provide a circulator unit, which is easily manufactured.
This object has been accomplished by the subject matter of claim 2.
It is another objet to provide a circulator, which allows for strip-line configuration.
This object has been accomplished by claim 3.
It is a further object to provide a circulator that has strong and inflexible structure and which furthermore can be produced very cost efficiently.
This object has also been accomplished by the subject matter of claim 3.
It is another object to provide a circulator network, which for instance may be used for a phase array antenna.
This object has been accomplished especially by the subject matter according to claims 6, 7 and 10.
Further advantages will appear from the following detailed description of the invention.